Biofilm refers to the complex, sessile communities of microbes found either attached to a surface or buried firmly in an extracellular matrix as aggregates. The biofilm matrix surrounding bacteria makes them tolerant to harsh conditions and resistant to antibacterial treatments. Moreover, the biofilms are responsible for causing a broad range of chronic diseases and due to the emergence of antibiotic resistance in bacteria it has really become difficult to treat them with efficacy. Furthermore, the antibiotics available till date are ineffective for treating these biofilm related infections due to their higher values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), which may result in in-vivo toxicity. Hence, it is critically important to design or screen anti-biofilm molecules that can effectively minimize and eradicate biofilm related infections. In the present article, we have highlighted the mechanism of biofilm formation with reference to different models and various methods used for biofilm detection. A major focus has been put on various anti-biofilm molecules discovered or tested till date which may include herbal active compounds, chelating agents, peptide antibiotics, lantibiotics and synthetic chemical compounds along with their structures, mechanism of action and their respective MICs, MBCs, minimum biofilm inhibitory concentrations (MBICs) as well as the half maximal inhibitory concentration (IC50) values available in the literature so far. Different mode of action of anti biofilm molecules addressed here are inhibition via interference in the quorum sensing pathways, adhesion mechanism, disruption of extracellular DNA, protein, lipopolysaccharides, exopolysaccharides and secondary messengers involved in various signaling pathways. From this study, we conclude that the molecules considered here might be used to treat biofilm-associated infections after significant structural modifications, thereby investigating its effective delivery in the host. It should also be ensured that minimum effective concentration of these molecules must be capable of eradicating biofilm infections with maximum potency without posing any adverse side effects on the host.

https://www.tandfonline.com/doi/pdf/10.1080/21505594.2017.1313372

Strategies for combating bacterial biofilms: A focus on anti-biofilm agents and their mechanisms of action

Phytochemicals for human disease: An update on plant-derived compounds antibacterial activity

Decreased antimicrobial efficiency has become a global public health issue. The paucity of new antibacterial drugs is evident, and the arsenal against infectious diseases needs to be improved urgently. The selection of plants as a source of prototype compounds is appropriate, since plant species naturally produce a wide range of secondary metabolites that act as a chemical line of defense against microorganisms in the environment. Although traditional approaches to combat microbial infections remain effective, targeting microbial virulence rather than survival seems to be an exciting strategy, since the modulation of virulence factors might lead to a milder evolutionary pressure for the development of resistance. Additionally, anti-infective chemotherapies may be successfully achieved by combining antivirulence and conventional antimicrobials, extending the lifespan of these drugs. This review presents an updated discussion of natural compounds isolated from plants with chemically characterized structures...

Plant Natural Products Targeting Bacterial Virulence Factors

Efflux pumps are widely implicated in antibiotic resistance because they can extrude the majority of clinically relevant antibiotics from within cells to the extracellular environment. However, there is increasing evidence from many studies to suggest that the pumps also play a role in biofilm formation. These studies have involved investigating the effects of efflux pump gene mutagenesis and efflux pump inhibitors on biofilm formation, and measuring the levels of efflux pump gene expression in biofilms. In particular, several key pathogenic species associated with increasing multidrug resistance, such as Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus, have been investigated, whilst other studies have focused on Salmonella enterica serovar Typhimurium as a model organism and problematic pathogen. Studies have shown that efflux pumps, including AcrAB-TolC of E. coli, MexAB-OprM of P. aeruginosa, AdeFGH of A. baumannii and AcrD of S. enterica, play important roles in biofilm formation. The substrates for such pumps, and whether changes in their efflux activity affect biofilm formation directly or indirectly, remain to be determined. By understanding the roles that efflux pumps play in biofilm formation, novel therapeutic strategies can be developed to inhibit their function, to help disrupt biofilms and improve the treatment of infections. This review will discuss and evaluate the evidence for the roles of efflux pumps in biofilm formation and the potential approaches to overcome the increasing problem of biofilm-based infections.

/pdf/role-of-bacterial-efflux-pumps-in-biofilm-formation-42bz8ra285.pdf

Role of bacterial efflux pumps in biofilm formation.

The majority of current infectious diseases are almost untreatable by conventional antibiotic therapy given the advent of multidrug-resistant bacteria. The degree of severity and the persistence of infections are worsened when microorganisms form biofilms. Therefore, efforts are being applied to develop new drugs not as vulnerable as the current ones to bacterial resistance mechanisms, and also able to target bacteria in biofilms. Natural products, especially those obtained from plants, have proven to be outstanding compounds with unique properties, making them perfect candidates for these much-needed therapeutics. This review presents the current knowledge on the potentialities of plant products as antibiotic adjuvants to restore the therapeutic activity of drugs. Further, the difficulties associated with the use of the existing antibiotics in the treatment of biofilm-related infections are described. To counteract the biofilm resistance problems, innovative strategies are suggested based on literature data. Among the proposed strategies, the use of phytochemicals to inhibit or eradicate biofilms is highlighted. An overview on the use of phytochemicals to interfere with bacterial quorum sensing (QS) signaling pathways and underlying phenotypes is provided. The use of phytochemicals as chelating agents and efflux pump inhibitors is also reviewed.

/pdf/new-perspectives-on-the-use-of-phytochemicals-as-an-emergent-1yfh8169ga.pdf

New Perspectives on the Use of Phytochemicals as an Emergent Strategy to Control Bacterial Infections Including Biofilms.

Klebsiella pneumoniae, an important opportunistic pathogen, exists as a biofilm in persistent infections and in-dwelling medical devices. With the objective of identifying natural compounds inhibiting biofilm formation in K. pneumoniae, 35 clinical isolates were screened,out of which 7 strong biofilm producers were identified. Six natural compounds were tested for their inhibitory effects on bacterial growth and biofilm formation by determining the minimum inhibitory concentration and minimum concentration for biofilm inhibition (MBIC) for each compound. The results show that reserpine followed by linoleic acid, were the most potent biofilm inhibitors. Reserpine, an efflux pump inhibitor was effective at biofilm inhibition at a concentration of 0.0156 mg/mL, 64-fold lower concentration than its MIC. Linoleic acid, an essential fatty acid was effective as a biofilm inhibitor at 0.0312 mg/mL, which is 32-fold lower than its MIC. Berberine, another plant derived antimicrobial, chitosan and eugenol had an MBIC value of 0.0635 mg/mL. Curcumin, a natural phenolic compound was effective at biofilm inhibition at a concentration of 0.25 mg/mL, which is 50 fold less than its MIC. Notably, the MIC and MBIC data on these 6 natural compounds was reproducible in all seven high biofilm forming isolates of K. pneumoniae. The present report is a comprehensive comparative analysis of the dose dependent inhibition of various natural compounds on biofilm formation in K. pneumoniae.

http://nopr.niscair.res.in/bitstream/123456789/21073/1/IJEB%2051%289%29%20764-772.pdf

Identification of natural compounds which inhibit biofilm formation in clinical isolates of Klebsiella pneumoniae.

Identification of plasmid-mediated quinolone resistance genes qnrA1, qnrB1 and aac(6')-1b-cr in a multiple drug-resistant isolate of Klebsiella pneumoniae from Chennai

Problem statement: An increased resistance to antibiotics has 
been reported in Klebsiella pneumoniae, an opportunistic gram negative pathogen 
belonging to Entrobacteraceae due to the evolution and spread of plasmid encoded 
extended spectrum beta lactamases and other genes conferring cross-resistance 
to other antibiotics. This is of concern due to the increasing cost of antibiotic 
treatment and the spread of multidrug resistance to more pathogenic microorganisms. 
This study was undertaken to analyze the extent of the problem, to identify the 
most prevalent MDR isolates of Klebsiella pneumoniae in Chennai and to identify 
new plant based drugs. Approach: About 188 clinical isolates 
of Klebsiella pneumoniae were collected from Chennai during the period Nov. 2007-Oct. 
2008 and their resistance to different groups of antibiotics were analyzed. These 
isolates were further characterized by molecular studies to identify the ESBL 
genes conferring the resistance phenotype. Plant extracts were tested against 
the MDR isolates to identify new treatment methods. Results: Our 
results showed that the combination therapy of clavulanic acid with cephalosporins 
and fluroroquinolones-norfloxacin and ciprofloxacin were the most effective antibiotics 
for treatment of Klebsiella pneumoniae infections. However resistance to clavulanic 
acid was increasing among the isolates (17%). All the isolates harbored a plasmid 
containing one or more of the genes for ESBL resistance. Plasmid isolation from 
the Isolates followed by ESBL PCR genotyping showed that CTX-M was present in 
75 % isolates and TEM in 73% isolates either alone or in combination with the 
other ESBL genes. SHV ESBL type was present only in 42% of isolates. We identified 
4 presumptive clonal spreads which were likely to be prevalent in India by clustering 
based on ESBL genotypic and antibiotic resistance. The isolates with both SHV 
and CTX were correlated with the most pathogenic and clavulanic acid resistant 
isolates. The extracts of Hemidesmus indicus and Terminalia arjuna had a significant 
antimicrobial activity against the MDR isolates. Conclusion: There 
was an increase in the spread of the ESBL genes and clavulanic acid resistance 
in the clinical isolates of Klebsiella pneumoniae in Chennai. Our data also supported 
a higher incidence of CTX-M genotype in India though the SHV genotype was associated 
with the most resistant forms of ESBL. Future research with separation of plant 
extracts to identify bioactive principles will pave the way for newer plant based 
antibiotics.

Identification of Clonal Clusters of Klebsiella pneumoniae Isolates from Chennai by Extended Spectrum Beta Lactamase Genotyping and Antibiotic Resistance Phenotyping Analysis

H Magesh

Papers

Identification of natural compounds which inhibit biofilm formation in clinical isolates of Klebsiella pneumoniae.

Identification of plasmid-mediated quinolone resistance genes qnrA1, qnrB1 and aac(6')-1b-cr in a multiple drug-resistant isolate of Klebsiella pneumoniae from Chennai

Identification of Clonal Clusters of Klebsiella pneumoniae Isolates from Chennai by Extended Spectrum Beta Lactamase Genotyping and Antibiotic Resistance Phenotyping Analysis